The present invention relates to automatic transmissions for vehicles, and more particularly to control systems for adjusting engine idle speed in a vehicle including an automatic transmission with a torque converter.
Vehicles such as automobiles, trucks, etc., typically include an internal combustion engine that is coupled by a hydraulic torque converter to an automatic transmission. The hydraulic torque converter includes a housing, a turbine, a stator and a pump. The housing is bolted to the flywheel of the engine. The housing rotates at the same speed as the engine. The pump includes fins that are attached to the housing. The fluid is directed by the fins radially outwardly into fins on the turbine, which causes the turbine to spin. The turbine is connected to the transmission. As a result, the hydraulic torque converter transfers engine torque to the transmission.
An engine control module (ECM) controls the internal combustion engine and modifies engine idle speed. The ECM modifies engine idle speed using idle air control (IAC), electronic throttle control (ETC), or other similar functions. The ECM typically receives the following control inputs: engine speed, transmission input speed, transmission temperature, transmission gear selector position, and vehicle speed. The transmission input speed is equal to a turbine speed of the torque converter.
Automatic transmissions typically include a gear selector for selecting non-drive transmission positions such as park or neutral and drive transmission positions such as reverse or forward. A garage shift occurs when the driver shifts the automatic transmission from a non-drive transmission position to a drive transmission position. When the garage shift occurs, the load on the engine increases significantly when the transmission has the ability to transmit torque from the engine to the drive wheels. The torque increase does not occur instantaneously. Rather, there is a time delay while the transmission engages a transmission input clutch. The time delay is a function of the transmission type, pump pressure, oil temperature and other factors. Additionally, the initial load presented by the transmission is usually greater than the steady-state load. In other words, more effort is required to initially shear and spin the transmission fluid in the transmission than to keep the transmission spinning. During the garage shift, the magnitude of the transmission load and its timing vary greatly. As a result of this variation, maintaining constant engine idle speed during the garage shift can be challenging for the ECM.
Referring now to FIG. 1, a poorly compensated garage shift is illustrated. Engine idle speed 10, transmission input speed 12, and engine idle speed compensation 14 as well as their respective timings are shown. The start of the garage shift occurs at 20 and ends at 22. A time delay indicated by arrow 26 occurs while the transmission is applying the transmission input clutch. As can be appreciated, the load of the transmission on the engine increases quickly as seen at 30 causing the engine speed to sag as can be seen at 32.
Conventional methods of compensating engine idle speed during the garage shift usually include closed-loop feedback systems that detect engine sag and subsequently increase engine idle speed. Other methods inhibit closed-loop idle control until the transmission load is present or use a fixed timing to anticipate the increased load requirement. Closed-loop systems require an engine speed sag to occur. Fixed timing is susceptible to transmission clutch engagement variations and may cause engine speed sag or flares.
A control system and method according to the present invention maintains a constant engine idle speed during a garage shift of an automatic transmission with a torque converter. An engine control module or other processor identifies when transmission input clutch fill occurs. The engine control module increases engine output based on when the transmission input clutch fill occurs and before a decrease in engine idle speed occurs.
In other features of the invention, memory that is associated with the engine control module latches turbine speed and speed ratio. The engine control module declares transmission input clutch fill if the latched turbine speed minus a current turbine speed is greater than a first calibration constant. The engine control module also declares transmission input clutch fill if the latched speed ratio minus a current speed ratio is greater than a second calibration constant.
In still other features, the engine control module increases the engine output after waiting a first time delay after the transmission clutch fill occurs. The engine control module adds steady-state and dynamic engine output boosts. The dynamic engine output boost compensates for initial shear load within the transmission. The engine control module reduces the dynamic boost over time at a first rate. The dynamic and the steady-state engine output boosts are related to transmission temperature. The steady-state engine output boost compensates for steady-state load of the automatic transmission.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.